INTROGRESSION OF Yr5a AND Yr15 YELLOW RUST RESISTANCE GENES INTO THE BORLAUG 100 BREAD WHEAT CULTIVAR

Abstract

Wheat (Triticum aestivum L.) production is affected by various biotic factors such as yellow rust caused by Puccinia striiformis f. sp. tritici. This pathogen has the potential to cause yield losses of up to 100 % if susceptible cultivars are infected in early growth stages. The best strategy for the management of this disease is the use of resistant genotypes. The objective of this study was to transfer the Yr5a and Yr15 genes from the Blanca Grande 515 population to the Borlaug 100 cultivar (recurrent parent) to obtain resistant lines while maintaining its agronomic characteristics. Three hundred eighty-nine lines were obtained from two and three backcrosses between Borlaug 100 and Blanca Grande 515, which were evaluated at the seedling stage and adult plant in the field against the CMEX14.25 isolate. The presence of the genes was corroborated with SNP molecular markers. Results indicated that Yr5a, previously reported in homozygous state in Blanca Grande 515, is actually heterozygous, so the number of positive lines for this gene was low compared to those positives for Yr15. The number of gene combinations found was lower than the expected and positive lines for the two genes of interest were found after the second backcross. Three lines were identified as having both Yr5a and Yr15 genes in homozygous condition, one similar to Blanca Grande 515 and another with both genes in heterozygous condition. Two of the first three lines also possess the Yr17 gene, from Borlaug 100, and phenotypically they were very similar to that cultivar, which shows that the backcross method is effective in transferring and accumulating genes to achieve durable resistance while maintaining the phenotype of the recurrent parent.